The present invention relates to direct energy conversion devices, particularly to the use of carbon aerogel electrodes in direct energy conversion devices, and more particularly to a fuel cell using carbon aerogel electrodes loaded with a noble catalyst such as platinum, and soaked with phosphoric acid, for example.
Direct energy conversion devices, such as fuel cells, typically use carbon composite electrodes, impregnated with platinum, rhodium, or other noble catalyst. These electrodes suffer from high polarization resistance, resulting in limited power capability. The problem associated with high polarization resistance is largely due to the rate limiting catalysis of the oxygen reduction reaction. Catalysis reaction rates are proportional to the surface area of the electrodes. A need exists to provide electrodes for fuel cells which reduce or eliminate the above problem.
Carbon aerogels are recognized as having high surface areas and excellent electrical conductivity, and can be fabricated with widely varying physical characteristics, as described and claimed in U.S. Pat. No. 5,260,855 issued Nov. 9, 1993, entitled "Supercapacitors Based On Carbon Foams". Other carbon aerogels are known, as exemplified by U.S. Pat. Nos. 4,806,290, 4,873,218 and 4,997,804.
It has been recognized that the problems relative to high polarization resistances of carbon composite electrodes used in fuel cells can be overcome by using carbon aerogel electrodes loaded with a noble catalyst, provided the carbon aerogel has a reactant/catalyst (R/C) ratio of about 50-400, and with a density of about 0.3 to 1.2 g/cc and surface area of about 400-1200 m.sup.2 /g. Thus, due to the very high surface areas and electrical conductivity of carbon aerogels, the present invention satisfies the above-mentioned need for improved electrodes for fuel cells.